1. Field of the Invention
Full-scale operation of the Clinton P. Anderson Meson Physics Facility at the Los Alamos Scientific Laboratory will provide significant quantities of 25-day .sup.82 Sr for clinical investigation. The short-lived daughter, 75-second .sup.82 Rb, is of value in biomedicine for circulation and perfusion studies as well as for myocardial imaging. A radiochemical separation procedure for the quantitative recovery and purification of spallation-produced .sup.82 Sr from proton-irradiated molybdenum targets has recently been developed. (See copending application entitled "Chemical Isolation of .sup.82 Sr from Proton-Irradiated Mo Targets" by Patrick M. Grant et al.)
The existence of a suitable .sup.82 Sr-.sup.82 Rb isotope generator is crucial to the utility of this radionuclidic system in nuclear medicine. While many effective strontium-rubidium separations have been implemented in such diverse fields as fission research, geochemical and cosmochemical chronology studies, and isotope production, few methods satisfy the stringent requirements of a potential biomedical radioisotope generator:
1. The system should be simple to operate.
2. Near-quantitative .sup.82 Rb yields should be obtained from the generator with each milking to maximize the system efficiency.
3. The generator must have extremely low strontium breakthrough per elution to minimize the amount of long-lived, boneseeking radiostrontium activities administered to the patient. Conditions 2 and 3 taken together denote a large Rb-Sr separation factor.
4. The generator milking time should be short in comparison with the .sup.82 Rb half life. This keeps the amount of in situ .sup.82 Rb decay small and therefore the effective overall .sup.82 Rb yield high.
5. The generator eluant must be compatible with biological systems or have the potential to be easily and rapidly made so. The very short half life of .sup.82 Rb precludes the performance of any detailed post-elution chemistry in the interest of efficient radiorubidium yields.
6. The system should have sufficient stability on a time scale of several .sup.82 Sr half lives to allow repetitive usage and a reasonable shelf life.
2. Prior Art
The only .sup.82 Sr-.sup.82 Rb biomedical generators of which the inventors are aware are systems that employ the weakly acidic cation-exchange resin, carrier-free .sup.82 Sr, and an automatic elution system for intravenous infusion. (Y. Yano and H. O. Anger, Journal of Nuclear Medicine 9: 412-415, 1968.) One generator uses varying strengths of ammonium acetate (NH.sub.4 C.sub.2 H.sub.3 O.sub.2) solution as the eluant, but it is restricted to concentrations .ltoreq. 0.4 M because of the toxicity of the acetate compound. The Rb-Sr separation factor for a fresh generator is 10.sup.4, but passage of 400 ml of 0.3 M NH.sub.4 C.sub.2 H.sub.3 O.sub.2 through the column reduces this value to 10.sup.2, and the .sup.82 Rb yield in a 20-ml elution is only 56 percent. Another generator elutes the .sup.82 Sr-loaded column with a 3 percent NaCl solution. This system exhibits a 10.sup.5 maximum Rb-Sr separation factor, no significant increase in strontium leakage with up to 600 ml of eluant, and a .sup.82 Rb elution yield of 62 percent.